12.1 Controlling Where Errors Appear

Many things can go wrong in your program that cause the PHP interpreter to generate an error message. You have a choice about where those error messages go. The messages can be sent along with other program output to the web browser. They can also be included in the web server error log.

A useful way to configure an error message display is to have the errors displayed on screen when you're developing a PHP program, and then sent to the error log once you're done development and people are actually using the program. While you're working on a program, it's helpful to see immediately that there was a parse error on a particular line, for example. But once the program is (supposedly) working so that your coworkers or customers can use it, such an error message would be confusing to them.

To make error messages display in the browser, set the display_errors configuration directive to On. To send errors to the web server error log, set log_errors to On. You can set them both to On if you want error messages in both places.

An error message that the PHP interpreter generates falls into one of five different categories:

Parse error

A problem with the syntax of your program, such as leaving a semicolon off of the end of a statement. The interpreter stops running your program when it encounters a parse error.

Fatal error

A severe problem with the content of your program, such as calling a function that hasn't been defined. The interpreter stops running your program when it encounters a fatal error.

Warning

An advisory from the interpreter that something is fishy in your program, but the interpreter can keep going. Using the wrong number of arguments when you call a function causes a warning.

Notice

A tip from the PHP interpreter playing the role of Miss Manners. For example, printing a variable without first initializing it to some value generates a notice.

Strict notices

An admonishment from the PHP interpreter about your coding style. Most of these have to do with esoteric features that changed between PHP 4 and PHP 5, so you're not likely to run into them too much.

You don't have to be notified about all the different error categories. The error_reporting configuration directive controls which kinds of errors the PHP interpreter reports. The default value for error_reporting is E_ALL & ~E_NOTICE & ~E_STRICT, which tells the interpreter to report all errors except notices and strict notices. Appendix A explains what the & and ~ mean in configuration directive values.

PHP defines some constants you can use to set the value of error_reporting such that only errors of certain types get reported: E_ALL (for all errors except strict notices), E_PARSE (parse errors), E_ERROR (fatal errors), E_WARNING (warnings), E_NOTICE (notices), and E_STRICT (strict notices).

Because strict notices are rare (and new to PHP 5), they are not included in E_ALL. To tell the PHP interpreter that you want to hear about everything that could possibly be an error, set error_reporting to E_ALL | E_STRICT.